Neuromuscular effects of acute 2,4-dichlorophenoxyacetic acid (2,4-D) exposure in dogs.

2,4-Dichlorophenoxyacetic acid (2,4-D) was administered once orally to adult female mongrel dogs at 0, 25, 50, 75, 100 or 125 mg/kg of body weight (n = 4 per group). Clinical neurological examinations, electromyography (EMG) and motor nerve conduction velocity measurements were carried out before exposure, and on days 1, 3, 7, 14, 21 and 28 post-exposure. On day 7, two dogs per group were killed. Samples of the medial and lateral plantar nerves were removed for teased fiber and semi-thin section analysis; samples of appendicular muscles were removed for histology and histochemistry. Necropsy included histopathological examination of the brain and spinal cord at multiple levels. Remaining dogs were killed on day 28 and their tissues were processed similarly. Transient generalized myotonic discharges were found in skeletal muscles of dogs receiving 50 mg/kg or more of 2,4-D. A few dogs in the higher dosage groups also had mild muscle stiffness, myotonic dimpling and/or lethargy, lasting up to 3 days post-exposure. Other parameters remained within normal limits.

Concomitant brainstem axonal dystrophy and necrotizing myopathy in vitamin E-deficient rats.

The purpose of this study was to simultaneously evaluate in rats the effects of vitamin E depletion on tissue alpha-tocopherol (alpha-T) concentrations, electrophysiologic measurements and histopathology. Rats (21-day-old male Wistar) were fed either vitamin E-deficient or supplemented (control) diets (n = 6/group) for 10, 16, and 61 weeks. At these times, electrophysiologic tests (electromyography, spinal and somatosensory evoked potentials, and motor nerve conduction velocity) were performed, the rats were killed and alpha-T concentrations of adipose tissue, sciatic nerve, and cervical and lumbar spinal cord were measured along with histopathologic evaluation of skeletal muscles and the nervous system. By 61 weeks, depletion of alpha-T from adipose tissue and peripheral nerve was more severe (< 1% of controls) than from cervical and lumbar spinal cord (15 and 8% of controls, respectively). Electrophysiologic tests were normal at all times. Histopathologic evaluation at 61 weeks revealed normal peripheral nerve structure, but necrosis of type 1 muscle fibers and increased numbers of spheroids in the gracile and cuneate nuclei. Our results confirm that low alpha-T concentrations in tissues precede histologic changes in peripheral nerves and skeletal muscle. Furthermore, pathologic changes associated with vitamin E deficiency occur independently in muscle and nervous tissue of rats.

Depletion of adipose tissue and peripheral nerve alpha-tocopherol in adult dogs.

To assess the relationship between tissue alpha-tocopherol depletion and histopathologic or functional changes in nervous tissue, a longitudinal study of male 1-year-old beagle dogs, two fed a vitamin E-deficient diet (0.05 +/- 0.02 mg alpha-tocopherol/kg;--E dogs) and two fed a vitamin E-supplemented diet (114 +/- 14 mg alpha-tocopherol/kg; +E dogs), was carried out. Plasma and adipose tissue alpha-tocopherol concentrations, neurological examinations, and sensory and motor nerve conduction velocities were determined at approximately 8-wk intervals over 109 wk. Tibial nerve alpha-tocopherol concentrations were measured at 65 and 109 wk; adjacent sections were examined for histologic changes. In the two -E dogs, plasma alpha-tocopherols declined linearly on a semilog plot to < 0.1 microgram/mL by 109 wk. Plasma alpha-tocopherol concentrations were depleted to half of the initial concentrations in approximately 87 d. Adipose tissue alpha-tocopherol concentrations (based on wet weight, cholesterol or triglyceride) also declined linearly on semilog plots, and were depleted to half of the initial concentrations in approximately 120 d. Tibial nerve alpha-tocopherols (ng/microgram cholesterol) in -E dogs decreased to 16% of average +E at 65 wk, and to 2% at 109 wk. Neurologic examinations, histologies and nerve conduction velocities were normal in all dogs throughout the study. Our results demonstrate in dogs that depletion of plasma, adipose tissue and nerve alpha-tocopherol precedes histologic and functional changes in peripheral nerves during vitamin E deficiency.

Alpha-tocopherol concentrations of the nervous system and selected tissues of adult dogs fed three levels of vitamin E.

The effects of dietary vitamin E levels on tissue alpha-tocopherol (alpha-T) concentrations in different parts of the nervous system are largely unknown. Therefore, we measured the alpha-T contents of nervous and other tissues obtained from beagle dogs fed for two years a vitamin E-deficient diet (-E, 0.05 +/- 0.02 mg vitamin E/kg diet, n = 2), a vitamin E-supplemented diet (+E, 114 +/- 14 mg/kg, n = 2), or a standard chow diet (En, 74 +/- 6 mg/kg, n = 3). Brain regions and spinal cords of +E dogs contained about double the alpha-T concentrations of En dogs, and about 10-fold those of -E dogs. The various brain regions of -E dogs, compared with En dogs, retained 12-18% of the alpha-T concentrations, with the exception of the caudal colliculus, which retained 48%. Peripheral nerve alpha-T concentrations in +E dogs (67 ng/mg wet weight) were nearly 5-fold higher than in En dogs (13.4 +/- 5.9 ng/mg) and 80-fold higher than in -E dogs (0.8 ng/mg). Within each dietary group, the lowest alpha-T concentrations in the central nervous system (CNS) were in the spinal cord. Peripheral nerves were the most susceptible to vitamin E repletion or depletion: in +E dogs, nerves contained higher concentrations of alpha-T than most brain regions; in En dogs, they contained similar concentrations; but in -E dogs, they contained less alpha-T than most brain regions. Muscles and other tissues of -E dogs retained from 1 to 10% of En values.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin E deficiency in dogs does not alter preferential incorporation of RRR-alpha-tocopherol compared with all rac-alpha-tocopherol into plasma.

The plasma and lipoprotein transport of RRR and all rac-alpha-tocopherols, labeled with different amounts of deuterium [2R,4'R,8'R-alpha-[5-C2H3]tocopheryl acetate (d3RRR-alpha-tocopheryl acetate] and 2RS, 4'RS, 8'RS-alpha-[5,7-(C2H3)2]tocopheryl acetate (d6all rac-alpha-tocopheryl acetate), was studied in adult beagle dogs that had been fed a vitamin E-deficient (-E; two dogs) or supplemented (+E; two dogs) diet for two years. We set out to test the hypothesis that the activity of the hepatic tocopherol binding protein (which is thought to preferentially incorporate RRR-alpha-tocopherol into the plasma) is up-regulated by vitamin E deficiency. Labeled alpha-tocopherols increased and decreased similarly in plasma of both -E and +E dogs. Irrespective of diet, d3RRR-alpha-tocopherol was preferentially secreted in plasma. Thus, vitamin E deficiency in dogs does not markedly increase the apparent function of the hepatic tocopherol binding protein. We also studied vitamin E transport in a German Shepherd dog with degenerative myelopathy (DM). Based on the coincident appearance of d3RRR-alpha-tocopherol in plasma and chylomicrons, we suggest that the abnormality in DM may be associated with abnormal vitamin E transport resulting from an impaired function of the hepatic tocopherol binding protein.

Comparison of four erythrocyte fragility tests as indicators of vitamin E status in adult dogs.

Plasma alpha-tocopherol (alpha-T) concentrations, erythrocyte osmotic fragility and detergent sensitivity were measured at 8 week intervals in two 1-year-old male beagle dogs fed a vitamin E-deficient diet (< 0.08 mg per kg alpha-T) and in two control beagles fed the same diet supplemented with vitamin E (> 90 mg per kg alpha-T). Beginning at 24 weeks, dialuric acid haemolysis and spontaneous haemolysis were evaluated also. In the vitamin E-deficient dogs, plasma alpha-T concentrations declined progressively from baseline values of 20.5 and 31.3 micrograms per ml to 0.11 and 0.07 micrograms per ml, respectively, by 90 weeks. The supplemented dogs maintained alpha-T concentrations between 18.3 and 38.4 micrograms per ml. Both dialuric acid haemolysis (R = -0.89) and spontaneous haemolysis (R = -0.91) increased with declining plasma alpha-T concentration. In the dialuric acid haemolysis assay, 50 per cent haemolysis occurred when plasma alpha-T declined to 1.7 micrograms per ml, compared with spontaneous haemolysis in which 50 per cent haemolysis occurred when plasma alpha-T declined to 0.5 micrograms per ml. Osmotic fragility and detergent sensitivity remained unchanged in the vitamin E-deficient dogs throughout the study. Of the four tests, dialuric acid haemolysis was the most sensitive in-vitro assay for vitamin E deficiency in adult dogs.

Brain stem auditory-evoked response abnormalities in 14 dogs with confirmed central nervous system lesions.

Abnormal brain stem auditory-evoked responses (BAER) were recorded on 14 dogs with brain lesions confirmed by necropsy (n = 13) or magnetic resonance imaging and surgical biopsy (n = 1). Lesions included brain stem or cerebellar tumors (6 dogs), brain stem trauma (1 dog), forebrain tumors (3 dogs), hydrocephalus (2 dogs), granulomatous meningoencephalitis (1 dog), and meningoencephalitis (1 dog). Five affected dogs were comatose at the time of recording. BAER abnormalities could be classified as (1) absence of some or all of waves I to V, (2) increased latencies, with wave V being most frequently affected, or (3) a reduction in the amplitude ratio of waves V/I.

Insulinoma and subclinical peripheral neuropathy in two dogs.

Two dogs with diffuse, subclinical polyneuropathy associated with insulinoma are reported. Seizures were the dominant sign of central nervous system disease. One dog had clinical signs of facial nerve paralysis. Lesions in selected appendicular and cranial nerves included a mixture of demyelination, remyelination, and axonal degeneration. The incidence (range: 18-47%) of these changes far exceeded that of comparable nerves from six control dogs (range 0-11%). Myopathic and electrodiagnostic findings were compatible with the nerve changes.

Idiopathic polyneuropathy in Alaskan malamutes.

Clinical and morphologic features of a progressive polyneuropathy in young mature Alaskan Malamutes are described. Clinical signs included progressive paraparesis, synchronous pelvic limb gait, exercise intolerance, hyperesthesia, hyporeflexia, muscle atrophy, and tetraplegia. Electromyographic testing revealed diffuse fibrillation potentials and positive sharp waves in limb muscles, especially in muscles below the elbow and stifle. Pathologic findings in skeletal muscles and peripheral nerves included neurogenic muscle atrophy, focal or diffuse loss of myelinated nerve fibers, myelinoaxonal necrosis, and variable demyelination or remyelination. Ultrastructural changes included axonal degeneration, presence of numerous Büngner bands, and denervated Schwann cell subunits. The nature and distribution of abnormal electrophysiologic and pathologic findings were suggestive of a distal sensorimotor polyneuropathy, which we have termed idiopathic polyneuropathy of Alaskan Malamutes to distinguish this condition from hereditary polyneuropathy of Norwegian Alaskan Malamutes, last described in 1982.

Electroacupuncture in the treatment of chronic lameness in horses and ponies: a controlled clinical trial.

Electroacupuncture was used to treat lameness in horses and ponies with chronic laminitis (n = 10) or navicular disease (n = 10). A clinical trial was conducted with random allocation of equal numbers of animals to control and treatment groups. Acupuncture was performed three times per week for four consecutive weeks. The degree of lameness was assessed by 1) a grading scheme, 2) measurement of stride lengths and 3) analysis of weight distribution using a force plate. Although seven out of ten animals with chronic laminitis improved clinically during the trial, there were no statistically significant differences between treatment and control groups. Six out of ten horses with navicular disease improved, but there were no significant differences between treatment and control groups.

Effects of perinatal high dose dexamethasone on skeletal muscle development in rats.

Five litters of suckling rats were given either dexamethasone (DEX), 1 mg/kg, subcutaneously, three times daily (n = 4/litter) or vehicle control (n = 4/litter) from day 3 through day 7 after birth. Rats were weighed weekly and were weaned on day 30. On day 60, rats were killed and the soleus (SOL) and extensor digitorum longus (EDL) were removed for the following analyses: 1) wet weight, 2) light microscopic examination of hematoxylin and eosin stained transverse sections, 3) quantitative morphometric analysis of myosin ATPase stained transverse sections (fiber numbers, fiber type percentages and mean fiber diameters), and 4) DNA (total and mg/g wet weight). The following parameters were significantly reduced in treated rats: 1) body weight, 2) wet weight of SOL and EDL, and 3) mean diameter of SOL type I fibers. There was a trend for total DNA of SOL and EDL to be decreased in treated rats but this was not statistically significant. In a second experiment, pregnant rats (n = 4) were given DEX, 1 mg/kg, subcutaneously, twice daily, on days 17 and 18 of gestation. Two rats served as vehicle controls. The prenatally DEX-exposed rats weighed significantly less on weeks 3, 4, 6, 7 and 8. There were significant reductions in the following parameters for treated rats: 1) SOL wet weight, and 2) total number of SOL type I fibers. There was a trend for SOL DNA to be reduced but this was not statistically significant.

Inheritance of myotonic discharges in American quarter horses and the relationship to hyperkalemic periodic paralysis.

Electromyography (EMG) was used to detect myotonic discharges in Quarter Horse breeding stock and to follow the results of mating horses with hyperkalemic periodic paralysis (HPP). The studies were performed on two brood mare farms. A total of six breeding stock showed myotonic discharges and 15 were nonmyotonic. Myotonic discharges were seen in five of six horses belonging to the blood line previously implicated as being predisposed to HPP. Two of these horses had shown clinical signs of HPP. Only one of 15 breeding horses unrelated to the HPP predisposed blood line showed myotonic discharges. When both parents were non-myotonic on EMG than the F1 generation (n = 6) were also nonmyotonic. When a stallion with HPP and myotonic discharges was mated to eight nonmyotonic mares over a six year period half the animals of the F1 generation (n = 25) showed myotonic discharges. When both parents showed myotonic discharges four F1 offspring were myotonic and two were nonmyotonic on EMG testing. There was no evidence of sex linkage. The results are consistent with an autosomal dominant mode of inheritance. Hyperkalemic periodic paralysis and myotonic discharges on EMG may be different manifestations of the same underlying defect.

Linear regression to determine the relationship between F-wave latency and limb length in control dogs.

Minimal latencies of F waves were determined for the ulnar and sciatic-tibial nerves in 17 dogs of various breeds, weighing between 8 to 25 kg. A linear regression model was fitted to the data (r = 0.78 and 0.87, respectively), so that latencies could be predicted despite the large variation in limb lengths among different breeds of dogs.

Effect of disulfiram in experimentally induced vitamin E deficiency myopathy in lambs.

Vitamin E deficiency myopathy (white muscle disease) was induced in 14 suckling lambs (2 experiments; 7 lambs/experiment) by addition of cod liver oil to the diet. Disulfiram, an antioxidant, was administered orally once each day to 8 of the 14 lambs at 2 different doses. Serum creatine kinase (CK) activity was measured weekly for 5 weeks. Increased CK activity was evident in some lambs beginning at week 3. By week 4, serum CK was abnormally increased in 5 of the 6 nontreated lambs (ie, disulfiram not given) and in 4 of the 8 treated lambs. The combined disulfiram groups had significantly lower serum CK values during the study (P less than 0.05). Serum alpha-tocopherol, measured on samples from week 5 for lambs of experiment 1, was significantly higher in treated lambs (P less than 0.01). Microscopic examination of the vastus lateralis muscle indicated that the most severe lesions, consistent with nutritional myopathy, were seen in nontreated lambs. Therefore, disulfiram may have an antioxidant effect in lambs with vitamin E deficiency.

Effect of electromyography on serum creatine kinase values in clinically normal dogs and horses.

The effect of needle electromyography (EMG) on serum creatine kinase (CK) activity was determined, using clinically normal dogs (males and females; n = 8) and horses (females; n = 8). All animals appeared normal on EMG evaluation. Serum CK was measured before and 4, 24, and 48 hours after EMG. Except for a single 24-hour sample in a dog, the animals did not have abnormally increased serum CK activity after EMG. For dogs and horses, mean values were increased, but within normal range at 4 and 24 hours and returned to base-line values by 48 hours after EMG. For dogs, but not for horses, these CK increases at 4 and 24 hours were significant (P less than 0.05). Most dogs and horses, without neuromuscular disease, did not have serum CK activity above the normal range after EMG.

Correlation of brain stem auditory-evoked responses with cranium size and body weight of dogs.

Brain stem auditory-evoked responses were recorded in 9 male and 11 female clinically normal mature dogs, weighing between 2 and 36 kg. Mean wave latency for the entire group of dogs, using 60-dB hearing level click stimuli at 11/s for waves I to VII was: 1.41, 2.21, 2.85, 3.31, 3.71, 5.12, and 6.46 ms, respectively. The mean interpeak latency for waves I and V (IPLIV) was 2.32 ms. Neither gender nor ear effect was detectable. Positive correlation was observed between cranium length, cranium width, nasion-external auditory meatus interval, and body weight for wave-V latency and IPLIV. Such correlation was not documented for wave I. The regression equations for their effects on IPLIV were: cranium length, y = 0.05x + 1.85; cranium width, y = 0.07x + 1.32; nasion-external auditory meatus interval, y = 0.05x + 1.79; and body weight, y = 0.01x + 2.15. On the basis of any of the 3 variables of cranium size or body weight, the study population could be classified into groups of large and small dogs, with the large group having significantly (P less than 0.05) longer latency for wave V and IPLIV. It is recommended that the effect of size variation in dogs on brain stem auditory-evoked responses should be compensated for by use of the regression equation based on cranium length.

Electromyographic evaluation of conduction time and velocity of the recurrent laryngeal nerves of clinically normal dogs.

In 25 adult dogs of various breeds, recurrent laryngeal nerve fibers were electrically stimulated at 2 points along their extralaryngeal course. Evoked compound muscle action potentials were recorded in the ipsilateral intrinsic laryngeal muscles, using a percutaneous needle electrode. Latencies, amplitudes, and durations were measured. Latencies were correlated with neck length (r = 0.88 on left and 0.82 on right). Five of the dogs were euthanatized, and the nerve length between the 2 stimulating needle electrodes was measured; calculated conduction velocities (mean +/- SD) were 55 +/- 6 m/s (left) and 57 +/- 6 m/s (right). In 38 additional canine cadavers, the lengths of the exposed left and right recurrent laryngeal nerves were correlated with neck length (r = 0.44 on left and 0.56 on right). A linear regression model is proposed for predicting normal latencies, despite variations in neck length among different breeds of dogs.

Maturation of spinal-evoked potentials to tibial and ulnar nerve stimulation in clinically normal dogs.

Spinal-evoked potentials were recorded from 2 litters of clinically normal mixed-breed dogs between 35 and 300 days of age. Summated responses to tibial nerve stimulation were recorded from percutaneous needle electrodes placed at L7-S1, L4-5, T13-L1, C7-T1, and the cisterna cerebellomedullaris. The ulnar nerve was stimulated with recordings at C7-T1 and the cisterna cerebellomedullaris. Amplitudes did not change significantly with age, but were significantly (P less than 0.05) different between various recording sites. On day 35, segmental and overall (L7-cisterna cerebellomedullaris) conduction velocities were less than half of the adult values. Spinal cord conduction velocities increased with age, reaching adult values at approximately 9 months of age. It was determined that quadratic equations best predicted the conduction velocities during maturation.

Ground reaction forces in Greyhounds with tibial nerve injury.

OBJECTIVES: To measure ground reaction force variables during lameness resulting from impaired tibial nerve function and to determine whether these variables changed significantly as recovery progressed. ANIMALS: 11 healthy Greyhounds of either sex, weighing between 22 and 39 kg. PROCEDURE: On 3 consecutive days before surgery, ground reaction forces were measured by force platform gait analysis at the trot. In dogs under general anesthesia, the left tibial nerve was crushed proximal to innervation of the gastrocnemius muscle. Gait analyses were repeated on days 8 to 10, 28 to 30, 43 to 45, 58 to 60, and 90 to 92 after surgery. Ground reaction force variables and stance time were compared among the 3-day clusters. RESULTS: 10 days after surgery, all dogs had weight-bearing lameness attributed to paralysis of muscles in the caudal compartment of the crus. Nerve regeneration resulted in functional recovery within 3 months. Decreases in vertical force were significant 10 days after surgery; thereafter, changes reflected gradual return of load bearing, with the most marked improvement between 10 and 45 days. At 90 days, vertical force variables were within 3% of presurgical values. Stance time for the left hind limb was significantly longer at 10, 30, and 45 days after surgery and was seen in all dogs, but returned to within 1 % of preoperative stance time at 90 days. The effect of tibial nerve dysfunction on braking or propulsive force was not significant. CONCLUSIONS AND CLINICAL RELEVANCE: The significant changes in vertical ground reaction forces in hind limbs of dogs during lameness that resulted from impaired tibial nerve function are detectable, as is response during recovery, by use of force platform analysis.

Effect of coat on rate of temperature increase in muscle during ultrasound treatment of dogs.

OBJECTIVE: To determine effect of coat during ultrasound treatment and to establish a protocol to achieve adequate thermal effects. ANIMALS: 9 healthy adult dogs. PROCEDURE: A standardized area was treated on the semitendinosus muscle of sedated dogs. Needle thermistors were inserted in the biceps femoris muscle to depths of 5 and 10 cm and in the ultrasound gel in the treatment area. Each dog was given 4 randomized 10-minute treatments (intensities of 0.5, 1.0, 1.5, and 2.0 W/cm2). Temperatures were measured at 30-second intervals during treatment and at 1- to 2-minute intervals after treatment. RESULTS: Baseline temperatures (mean+/-SD) were 30.6+/-1.8 C for coat, 38.2+/-1.2 C at a depth of 5 cm, and 39.0+/-0.7 C at a depth of 10 cm. At the 5-cm depth, an increase of > 1.6 C was obtained only with the maximum intensity when coat was clipped. Treatment with maximum intensity through short and long coats yielded mean increases at a depth of 5 cm of 0.7 and 0.4 C, respectively. Temperature at the 10-cm depth increased < 0.6 C for all treatments. Temperatures within the coat increased approximately 8.3 C and 22.2 C for short and long coats, respectively, with intensities of 1.5 and 2.0 W/cm2. CONCLUSIONS: Ultrasound treatment applied through an intact coat considerably warmed the coat with loss of thermal effects in underlying tissues. Inappropriate heating was apparently affected by selection of intensity, duration, and size of treatment area. CLINICAL RELEVANCE: Coat can impede successful use of ultrasound treatment of dogs.